Electric discharge device



Nov. 10, 1936. D. D. KNOWLES ELECTRIC DISCHARGE DEVICE Filed July 30, 1932 "ININYENTOR Dewey D. Knowls.

1 ATTO EY WIFSES:

Patented Nov. 10, 1936 UNITED STATES PATENT OFFICE ELECTRIC DISCHARGE DEVICE of Pennsylvania Application July 30, 1932, Serial No. 626,847

5 Claims.

My invention pertains to an electrical discharge device and especially to a grid controlled gaseous discharge tube having two cathodes.

In previous grid controlled gaseous discharge tubes which have utilized only a cold cathode, the current required in the grid circuit was quite small, practically zero, and a tube of extreme sensitivity was obtained. The current carrying capacity of this tube was, however, so limited that it could not be directly utilized to accomplish the control desired, and for most purposes it was necessary to provide a stage of amplification and/or a relay.

In grid controlled gaseous discharge tubes utilizing a heated cathode, a much greater current carrying capacity Was obtained and the tubes could be directly utilized to effect the control desired. In such tubes, however, the sensitivity was very much diminished by the presence of the hot cathode since an appreciable current was required in the grid circuit.

It is accordingly an object of my invention to obtain in one tube the combined advantages of high sensitivity and high current carrying capacity.

It is also an object of my invention to provide a high power tube which will be sensitive enough to operate directly from a photo-cell or by ca pacity.

In accordance with my invention, I provide a gaseous discharge tube with two cathodes, one of which is cold and the other of which is heated, or electron emitting. The two cathodes are so disposed with reference to the control grid and the anode. that until the tube glows it is essentially'a cold cathode tube, and thereafter the reduction of the space charge around the cold cathode allows the hot cathode to become effective and thereby greatly increase the current, to such an extent that various devices may be controlled directly without the interposition of relays or amplifiers.

The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments, when read in connection with the accompanying drawing, in which I Figure 1 is a view showing a longitudinal section of one embodiment of my invention,

Fig. 2 is a view diagrammatically representing the circuits and the elements of a system Where in my invention is applied,

Fig. 3 is a view showing a modification thereof, and

Fig. 4 is a view showing a longitudinal section of another embodiment of my invention.

Referring more specifically to Fig. 1 of the 5 drawing, my invention comprises a tube, or container l, which is evacuated in any well known manner, and is charged with a small quantity of one of the. rare gases, such as neon, to a pressure of about 2 to 10 millimeters of mercury absolute. 10- A pair of conductors 2 and 3, which support a filament 4, are sealed in a press or seal 5 in the upper end of the tube I. The filament 4 may be any well known form of bare or oxide coated filament.

A press or seal 6 rising from the lower end of the tube is provided with glass sleeves l and 8 which project upwardly into the tube. A conductor ll, comprising the anode electrode, extends through one of the glass sleeves l to the 20 inner end thereof. A second conductor l2, com prising the control grid, extends through the other glass sleeve 8 into the interior of the tube where it extends in enclosing relation adjacent to the inner end of the anode l l, at a distance preferably less than the mean-free-path of an electron in the gas, at the pressure established therein.

A metallic casing l3 preferably of cylindrical formation, is supported in enclosing spaced relation over the anode II and control grid l2 on a pair of supports I4 and H: which are sealed in the press 6 in any suitable manner. One of said supports M may have an extension l6 which passes from the tube I through the press. The 35 upper end of the metallic casing I3 is closed by a fine nickel screen 11.

A base (not shown) may be cemented to the bottom of the tube to provide plug-in prongs in a manner well known in the art. Circuit conductors may be connected by soldering, or in any well known manner, to the filament conductors 2 and 3 extending from the top of the tube. If desired, the filament may be omitted and the tube I may be provided with a branch containing a mercury pool which may be utilized as the electron emitting cathode.

As shown in Fig. 2, the cylindrical metallic casing I3 may be connected to the filament or electron emitting cathode by an internal conductor 18 thereby eliminating one of the leads [6 passing from the lower end of the tube.

In the utilization of my device, the electron emitting cathode 4 is connected by conductors 2 and 3 to the secondary winding 2| of a suitable transformer T from which it is energized, as shown in Fig. 2. The positive terminal of a source of potential 22 is connected by a conductor 23 to the electrode I I which constitutes the anode. The negative terminal of the potential source 22 is connected through any desired translating device 24, a ballast resistor RI and a conductor 25 to the filament 4 which comprises the hot cathode. This connection also extends by way of the conductor I8, to the metallic casing I3 which comprises the cold cathode. The ballast resistor RI may be omitted if. the impedance of the translating device is suitable.

The anode II is preferably grounded as at 26. The control grid I2 is preferably connected by a conductor 21 and a switching device 28 through a variable impedance or resistor R2 to ground 29. It is to be understood, however, that the grounds may be omitted and the anode II and grid I2 may be directly connected by a conductor. Either the switching device 28 or the variable impedance R2 may be actuated by a device responsive to the occurrence of certain conditions or the happening of a certain event upon which it is desired to energize the translating device 24.

Under normal conditions the control grid I2 is either open circuited by the contacting device 28, or if this is merely a manual switch which is closed, the grid is practically open circuited by the variable resistor R2 which, under normal conditions, has its resistance adjusted to a very high value. Under this condition the first flow of electron current from the cathode I3 results in an accumulation of electrons on the insulated control grid I2 which causes it to block the flow of further electron current. Under this condition, the translating device 24 is not energized since there is practically no current flowing.

When the predetermined condition or event occurs, the control grid I2 is practically connected to ground through the variation of resistor R2 to a very low order, or the closing of. contactor 28. The electron charge on the grid I 2 is thereby permitted to leak away and a permanent difference of potential is established between the grid I2 and the cathode I3 which results in a breakdown of the tube.

During the threshold discharge, or the breakdown period, space charges around the screen I'I complete the enclosure I3 so that the hot cathode 4 has no effect.

As soon as the tube breaks down, as a cold cathode tube, the large density of ionization results in a collapse of the space charge layers surrounding the screen I1 and the discharge passes through the screen. A large electron current then flows from the hot cathode 4 which is sufficient to directly energize the translating device 24 without amplification or relays, and the voltage drop across the tube is reduced to a low value thereby decreasing, or practically eliminating, sputtering of the cold cathode I3. The translating device 24 may comprise any regulating or signalling device which it is desired to control.

The embodiment shown in Fig. 1, wherein an internal conductor is not connected between the two cathodes within the tube, may be utilized in such a circuit as that disclosed in Fig. 2 by providing an equivalent external connection. However, the device may also be utilized without connecting the cathodes directly together, and different sources of current may be connected between the anode and the respective hot and cold cathodes. As shown in Fig. 3, a source of current such as a transformer TI may be connected between the anode I I and the cold cathode I3, and a separate source of current such as a second transformer T2 may be connected between the anode II and the heated cathode 4.

In Fig. 4 I have shown a modification of my device wherein the cold cathode comprises a flat disk 3!, of screen or perforated plate, which extends completely across the interior of the tube I between the hot cathode filament 4 and the other electrodes of the tube. The disk 3| is connected by a suitable internal conductor 32 to the filament 4. The operation of this embodiment of my invention is similar to the operation of the first embodiment as previously set forth.

It will be seen that I have provided a double cathode, grid controlled, gaseous discharge device having the combined characteristics of the extremely high sensitivity of a cold cathode tube, and the high current carrying capacity of a hot cathode tube.

Although I have shown and described certain embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except as is necessitated by the prior art and the scope of the appended claims.

I claim as my invention:

1. In combination a gaseous discharge device comprising an anode, a control grid adjacent thereto, a cathode remotely disposed and adapted to be heated, means for energizing said cathode, a cold cathode comprising an enclosing casing surrounding said anode and grid, the wall of said casing adjacent the energized cathode having an open mesh area, a translating device, a source of current connected between the anode and said energized cathode through said translating device, a source of current connected between the anode and said cold cathode, and a potential varying circuit connecting said control grid and anode.

2. In combination, a gaseous discharge device comprising an anode, a control grid adjacent thereto, a cold cathode interposed in the discharge path extending from said anode, said cathode having a large surface with at least one discharge opening therethrough, a second cathode outside the discharge path between said anode and said first-mentioned cathode, means for initiating a point-to-plane discharge between said anode and said cold cathode, said discharge energizlng the discharge path between said anode and said second cathode and an output circuit connecting said anode and said second cathode.

3. In combination, a gaseous discharge device comprising an anode, a control grid within the region of the order of the mean free path of an electron from said anode, a cold cathode interposed in the discharge path extending from said anode, said cathode having a large surface with at least one discharge opening therethrough, a second cathode outside the discharge path between said anode and said first-mentioned cathode, means for initiating a point-to-plane discharge between said anode and said cold cathode, said discharge energizing the discharge path between said anode and said second cathode and an output circuit connecting said anode and said second cathode.

4. In combination, a gaseous discharge device comprising an anode, a control grid adjacent thereto, a cold cathode interposed in the discharge path extending from said anode, said cathode comprising a casing about said anode and having a screen portion therein, a second cathode outside the discharge path between said anode and said first-mentioned cathode, means for initiating a point-to-plane discharge between said anode and said cold cathode, said discharge energizing the discharge path between said anode and said second cathode and an output circuit connecting said anode and said second cathode.

5. In combination, a gaseous discharge device comprising an anode, a control grid adjacent thereto, a cold cathode interposed in the discharge path extending from said anode, said cathode having a large surface with at least one discharge opening therethrough, a second cathode outside the discharge path between said anode and said first-mentioned cathode, and having an electron emissive coating, means for initiating a point-to-plane discharge between said anode and said cold cathode, said discharge energizing the discharge path between said anode and said second cathode and an output circuit connecting said anode and said second cathode. 10

DEWEY D. KNOWLES. 

